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1982 - 1991 Corvette: Service Bulletin: Information on State Emission Testing For All Models

Subject: INFORMATION ON STATE EMISSION TESTING FOR ALL MODELS
Model and Year:1982-91 ALL PASSENGER CARS AND TRUCKS
Source: Chevrolet Service Bulletin
Bulletin Number: 91-344-6E - (06/11/1991)

THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 91-57-6E, DATED AUGUST 1990. SPECIFIC PROCEDURES HAVE BEEN ADDED FOR TRUCKS ABOVE 8500 GVW. ALL COPIES OF 91-57-6E SHOULD BE DISCARDED.

With more emphasis being placed on air quality, many states and municipalities have instituted vehicle inspection/maintenance (I/M) programs, most of which include tailpipe exhaust emissions testing. (DIVISION) desires to do its part both in helping achieve cleaner air and in making sure our customers' vehicles are tested in a satisfactory manner.

PASSENGER CARS AND TRUCKS BELOW 8500 GVW.

A satisfactory exhaust emissions test includes making sure the vehicle's engine and emission control systems are fully warmed up just prior to conducting the test. An engine coolant temperature gauge that reads operating temperature or a warm radiator hose does not necessarily mean the vehicle is ready to be tested. For example, although the engine coolant temperature gauge may be reading at operating temperature, the catalytic converter may not be fully warmed up, which may cause exhaust emissions levels to be artificially high and not representative of whether the vehicle's emission control systems are functioning properly. Therefore, if the vehicle has been turned off or sitting at idle for several minutes, even though the engine coolant temperature gauge indicates the engine is at operating temperature, the vehicle should be driven on the road for a few minutes just prior to starting the official test to ensure that the engine and emission control systems are fully warmed up. An alternative warm up method that can be used and may be more convenient is running the engine at about 2500 rpm for two or three minutes with the transmission in park or neutral.

TRUCKS ABOVE 8500 GVW (NA4)

The use of the L19 (454 cu. in.) engine in any truck or van model above (8500 GVWR) should be preconditioned by driving the vehicle at highway speeds (40-55 MPH) for at least 15 minutes before conducting a state emission test. This will allow the emission control system to be fully warmed up.

Vehicles above 14,000 GVWR should be preconditioned the same as vehicles above 8501 GVWR if empty or lightly loaded. Vehicles above 14,000 GVWR can be preconditioned a shorter time and. at a lower speed if loaded.

Note: If vehicles are forced to idle for over 5 minutes while awaiting a state emission test, particularly in cold ambient temperatures, the vehicle should be preconditioned again before a test is conducted. Preconditioning should be considered at least once, in the event of a failed test.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.

© Copyright General Motors Corporation. All Rights Reserved

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